The number of possible stereoisomers for a compound containing three different chiral centers is .............

Which of the following cannot be given to exemplify a chiral structure?

In which of the following properties do the two enantiomers of lactic acid differ from each other?

The configurations of the carbon atoms $C_2$ and $C_3$ in the following compound are respectively:
$COOH-CH(OH)-CH(OH)-CHO$

The specific rotation of $(+)$-Mandelic acid is $+158^o$. What will be the specific rotation of a mixture containing $25\%$ $(-)$-Mandelic acid and $75\%$ $(+)$-Mandelic acid?

Provide detailed information about the relationship between optical activity and molecular structure.